I tried what you said start was 95-51 resting after 15 minutes. i got it up to 121 limped up the two flights of steps to oximeter it was 95-108 within one minute I was at 95 over 74. not really sure what any of it means. but my top to bottom differential was only 70 pretty pathetic to your range.
It's all relative to your health Funk. The easiest way to keep track is to see how much your pulse drops in 1 min after a few minutes of intense (or moderately intense) exercise. If after a few weeks of doing a routine your pulse drop is the same, you might want to add a rest day or two into your schedule. Exercise is like medicine- there is the right dose and there definitely is the possibility of overdosing.
I recommend to anybody who wants to gain cardio fitness to just do something continuous for 20-30 min, 3 days a week. But the key is to alternate what you do on each of those days. For example, day 1 you might want to do 1 min fast, 4 minute slow intervals, for 20 min. The next workout you might want to do 4 min moderate, 1 min easy intervals. Another workout might be just going very easy for 20 min.
An interval doesn't have to be and shouldn't be flat out, Just challenge yourself moderately. You want to feel challenged, not destroyed. If on any day you don't feel up to the workout, skip that day and do it the next.
After a few weeks you will start to see your pulse rate recovery over 1 min improve a lot.
A guy I used to ride with got a silver medal in the LA Olympic cycling road race. He taught me a lot- including not to go hard too often!